Field of the Invention
Various cans are conventionally formed of a cylindrical body portions with at least one separate end portion secured thereto to complete the can. It is necessary to seal the juncture between the can body and the can end with a sealant which must meet a number of demanding requirements. These requirements are particularly stringent with respect to cans employed as food containers. Compositions for sealing can ends have long been known. Originally, solid rubber gaskets were inserted in canning lids. These separate gaskets, although somewhat effective, were inconvenient from many viewpoints, including additional handling procedures and costs. Placing the gaskets within the lids was time consuming and did not permit high-speed formation of lids with a sealant.
Compositions were devised for formation of sealants directly on the canning lid. These compositions were deposited on the canning lids by various methods to provide high speed means of making can ends incorporating the sealing compound thereon.
Plastisol compositions are well known for such use as sealing compounds on can ends. However, plastisol compositions, as other compositions, display drawbacks and shortcomings including chemical reactivity with container contents, particularly where the composition imparts a taste or odor to food, poor pouring properties incompatible with high speed production, and instability of the composition resulting in short shelf life. Often such components were not resistent to heat degradation under conditions normally encountered during processing.
Other types of compositions utilized include emulsion systems. However, emulsion systems also experience one or more of the above problems, particularly instability in storage.
While emulsion systems are somewhat more stable in the presence of a solvent as opposted to the "dry" form, a dry composition is desirable for the shipping and storage accruing from the weight and bulk savings from such form. It is simple matter to blend the dry composition with the solvent at the time of use.
Summarily, the known sealants involve compromise between convenience, stability, taste inertness, chemical inertness in place, bulk and weight.